PEM format
PEM (Privacy-Enhanced Mail) format is the base64-encoded text container most TLS certificates, keys, and certificate signing requests are stored and exchanged in, wrapped between a "-----BEGIN ...-----" and "-----END ...-----" header naming the content type. The name comes from RFC 1421, an early-1990s standard for encrypting email that never saw wide adoption for its original purpose, but its text-safe encoding of binary cryptographic data was reused so widely for certificates and keys that RFC 7468 later formalized that reuse as its own specification, independent of email. The alternative is DER, the same underlying binary ASN.1 data PEM encodes, without the base64 and header wrapping; a file ending in .pem or .crt is usually PEM-encoded and readable as plain text, while a .der file is raw binary and can't simply be opened in a text editor. A CSR, a certificate, and a private key are all commonly distributed in PEM form, often concatenated in the same file for a full chain.
By AdminKit team, Netbase JSC · Updated